1. Field of the Invention
The present invention relates to a lens device and optical equipment using the same, such as a video camera or a digital still camera.
2. Description of the Related Art
It is known to prevent image blur due to handshake that tends to occur during a hand-held photo-taking operation using an image blur compensation unit, where the image blur compensation unit detects the state of blurring of a camera with a blur detecting unit and shifts a compensation lens in a direction orthogonal to the optical axis in accordance with the detected results.
In a camera provided with such an image blur compensation unit, displacement of an imaging position due to shake (blurring) is compensated for by movably supporting a compensation lens constituting at least a part of a photo-taking lens system and moving the compensation lens in a direction within a plane orthogonal to the optical axis of the main optical system so as to compensate for the shake (image blur).
In such an image blur compensation unit, an electromagnetic actuator is constructed of a coil and a magnet. One of the coil and the magnet is attached to a fixed portion (e.g., a fixed lens barrel) and the other one is attached to a lens holding frame for holding the compensation lens, so that relative movement of the lens holding frame may be directly achieved. When considering downsizing and power saving of the unit, it is advantageous to attach the magnet, which is heavier in weight, to the fixed portion and to attach the coil, which is lighter in weight, to the lens holding frame. In this configuration, wiring from the fixed portion to the coil mounted on the lens holding frame may be provided by a flexible printed board.
The position of a movable lens group for zooming or focusing is adjusted by rotating a screw portion provided on an output shaft of a stepping motor, so that a lens carrier frame connected to a rack member, which moves in conjunction with the screw portion, is moved in the direction of the optical axis.
In the case of the above-described related art, a stepping motor for driving the movable lens group for zooming and focusing controls the movable lens group so as to move and stop at a predetermined position by rotating a feed screw by an angle corresponding to a predetermined number of pulses.
In order to enhance resolution of the stop position of the movable lens group, it is necessary to reduce the pitch of the feed screw of the stepping motor. On the other hand, in order to increase the speed of movement of the movable lens group, the stepping motor may be rotated at a higher speed; in order to further increase the speed, it is necessary to increase the pitch of the feed screw. Therefore, simultaneous pursuit of increase in speed and improvement in accuracy is limited.
In particular, a simultaneous pursuit of stoppage with a high-degree of accuracy and movement of a focus lens at a high-speed is required due to the recent increase in pixel count of imaging elements and an increase in zoom ratio. Hence, a system realizing simultaneous pursuit of accurate control of lens stop positions and an increase in lens speed has been proposed, wherein a linear actuator including a coil and a magnet is used for moving the focus lens instead of a conventional stepping motor.
Such a linear actuator, however, has a lower generated torque than a driving mechanism using a stepping motor. Thus, the actuator cannot be disposed at a position too remote from the center of gravity of the movable lens group. Rather, the linear actuator must be disposed near the lenses in accordance with the amount of movement of the movable lens group. Consequently, in a construction in which an image blur compensation unit that drives a compensation lens in a direction orthogonal to the optical axis using an electromagnetic actuator and a linear actuator that drives a movable lens in a direction of the optical axis are disposed in a lens barrel, the effective arrangement of those actuators is an important issue.
In one aspect, the present invention relates to a lens device in which two actuators for driving a compensation lens in a direction orthogonal to the optical axis and an actuator for driving a movable lens in a direction of the optical axis are efficiently disposed in a space of the lens device, whereby downsizing of the lens device (lens barrel) and shortening of the length of the lens device (lens barrel) in the direction of the optical axis are achieved, the range of movement of the movable lens that moves in the direction of the optical axis is efficiently increased, and detection of the position of the movable lens in the direction of the optical axis is detected with a high-degree of accuracy.
In another aspect, the present invention related to an optical equipment using the same.
The in above-described drawbacks of the related art are overcome by a lens device of the present invention, which includes:
a blur compensation lens holding frame holding a blur compensation lens;
two blur compensation actuators that drive the blur compensation lens holding frame to move in a direction orthogonal to an optical axis of the lens device;
a movable lens holding member holding a movable lens; and
an axial driving actuator that drives the movable lens holding member in the direction of the optical axis;
wherein the axial driving actuator includes a magnet magnetized vertically in the direction of the optical axis, a yoke, and a coil mounted on the movable lens holding frame at a predetermined distance from the magnet and is movable in a direction of the optical axis by application of current in a direction orthogonal to a magnetic flux generated by the magnet, and
wherein the driving actuator is disposed at a position symmetrical to one of the two blur compensation actuators with respect to the optical axis when viewed in the direction of the optical axis.
In the lens device described above, the two blur compensation actuators are provided at respective positions in two different directions orthogonal to the optical axis (e.g., horizontal and vertical directions).
In this manner, the two actuators for driving the compensation lens in a direction orthogonal to the optical axis and the actuator for driving the movable lens in the direction of the optical axis efficiently may be arranged in a space of the lens device, thereby reducing a size of the lens device, shortening the length of the lens device in the direction of the optical axis, and efficiently and securely increasing the range of movement of the movable lens in the direction of the optical axis.
Optical equipment of the present invention includes:
an optical system including a movable lens axially movable in the direction of the optical axis, and a blur compensation lens that compensates for image blur by moving in a direction orthogonal to the optical axis;
two compensation actuators that drive the blur compensation lens holding frame in a direction orthogonal to the optical axis;
a driving actuator for driving the moving lens holding frame in the direction of the optical axis;
a light amount adjusting member that adjusts the amount of light passing through the optical system; and
an imaging element for imaging the optical image from the optical system;
wherein the driving actuator includes a magnet magnetized vertically in the direction of the optical axis, a yoke, and a coil mounted on a member holding the movable lens at a predetermined distance from the magnet and is movable in the direction of the optical axis by application of current in the direction orthogonal to the magnetic flux generated by the magnet, and
wherein the driving actuator is disposed at a position symmetrical to one of two blur compensation actuators that drive the blur compensation lens with respect to the optical axis when viewed in the direction of the optical axis.
In the optical equipment described above, the two blur compensation actuators are provided at respective positions in two different directions orthogonal to the optical axis. In addition, in the optical equipment described above, the one blur compensation actuator and the driving actuator are disposed between the light amount adjusting member and the imaging element.
In this arrangement, the two blur compensation actuators for driving the blur compensation lens in a direction orthogonal to the optical axis and the actuator for driving the movable lens in the direction of the optical axis efficiently may be arranged in a space of the optical equipment, thereby reducing the size of the optical equipment, shortening the length of the optical equipment in the direction of the optical axis, and effectively and securely increasing the range of movement of the movable lens in the direction of the optical axis.
According to the present invention, the optical system described above may employ a rear focus zoom lens constructed of four lens groups, with a first lens group including fixed positive lenses, a second lens group including negative variable power lenses for effecting zooming by moving in the direction of the optical axis, a third lens group including positive compensation lenses that compensate for image blur by moving a part of or all of the lenses in a direction orthogonal to the optical axis, and a fourth lens group including focus lenses movable in the direction of the optical axis that compensate for variations of image surface in association with the movement of the variable power lenses (the second lens group) and perform focus adjustment. The driving actuator described above may be used to move movable lenses, such as the variable power lens and the focus lens, in the direction of the optical axis.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.